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eliminating information that should not be there. This provides security for
the computers connected to your router, because computers from the
outside cannot access or send information directly to any computer on
your network. The router determines which computer the information
should be forwarded to and sends it. If the information is not intended for
any computer on your network, the data is discarded. This keeps any
unwanted or harmful information from accessing or damaging your
network.
Introduction to Firewalls
A firewall is a device that sits between your computer and the Internet that
prevents unauthorized access to or from your network. A firewall can be a
computer using firewall software or a special piece of hardware built
specifically to act as a firewall. In most circumstances, a firewall is used to
prevent unauthorized Internet users from accessing private networks or
corporate LAN’s and Intranets.
A firewall watches all of the information moving to and from your network
and analyzes each piece of data. Each piece of data is checked against a
set of criteria that the administrator configures. If any data does not meet
the criteria, that data is blocked and discarded. If the data meets the
criteria, the data is passed through. This method is called packet filtering.
A firewall can also run specific security functions based on the type of
application or type of port that is being used. For example, a firewall can
be configured to work with an FTP or Telnet server. Or a firewall can be
configured to work with specific UDP or TCP ports to allow certain
applications or games to work properly over the Internet.
Introduction to Local Area Networking
Local Area Networking (LAN) is the term used when connecting several
computers together over a small area such as a building or group of
buildings. LAN’s can be connected over large areas. A collection of LAN’s
connected over a large area is called a Wide Area Network (WAN).
A LAN consists of multiple computers connected to each other. There are
many types of media that can connect computers together. The most
common media is CAT5 cable (UTP or STP twisted pair wire.) On the
other hand, wireless networks do not use wires; instead they communicate
over radio waves. Each computer must have a Network Interface Card
(NIC), which communicates the data between computers. A NIC is usually
a 10Mbps network card, or 10/100Mbps network card, or a wireless
network card.
Most networks use hardware devices such as hubs or switches that each
cable can be connected to in order to continue the connection between
computers. A hub simply takes any data arriving through each port and
forwards the data to all other ports. A switch is more sophisticated, in that
a switch can determine the destination port for a specific piece of data. A
switch minimizes network traffic overhead and speeds up the communication over
